Tag Archives: radiation

Geiger counter – kit from the Far East

Loading

II am always fascinated by the topic of radioactivity. More precisely, it is the measurement or detection of this ionizing radiation, which is produced by the decay and of atomic nuclei with the release of energy. A basic distinction is made between the energy (alpha and beta particles) emitted by the movement of the decaying particles (i.e. particle radiation) and the radiation energy that is transported as an electromagnetic wave (gamma radiation and also X-rays). These types of radiation have different energy densities and ranges. Depending on the type, they are more or less easy to shield. Alpha radiation is particle radiation that is strongly slowed down by matter (air, water) and no longer penetrates a sheet of paper. However, these particles give off the energy over their very short distance. This is particularly dangerous if these particles are inhaled or radiate on the upper layers of the skin. Gamma radiation in turn penetrates matter very easily like a radio wave and can be shielded most effectively with lead. It goes without saying that this type of radiation is anything but harmless.

You cannot see, smell, taste or otherwise perceive this radiation directly, but the danger is still there. With relatively simple techniques, however, these decay processes can be made visible or audible and counted.

This has been done for a long time with a so-called counter tube or, thanks to modern technology, with semiconductors. A P-N junction is operated in reverse direction and the very small reverse current is measured with the exclusion of light (i.e. darkened). If high-energy radiation hits this P-N transition, the current flow is increased for a short time and can be detected.

Whenever the opportunity arises to get a detector very cheaply, I of course take it. So this time too. I had to look at a simple kit based on detection using a counter tube. The kit comes from the Far East and consists of a base board, an attached Arduino Nano and an LC display that is also attached.

All components required for detection are on the mainboard. This includes, among other things, the generation of high voltage for the counter tube, which is implemented using a simple boost converter circuit driven by a 555. To attach the counter tube to the mainboard, the designer of this board chose simple glass tube fuse holders. They don’t fit exactly, but they can be stretched so that they hold the counter tube firmly in place. Incidentally, the counter tube is a J305. It is approx. 90mm long and has a diameter of almost one centimeter.

The counter tube works with an anode voltage of 350V to 480V. Below I have listed the specifications from the data sheet:

  • Anode voltage: 350 v bis 480 V
  • Type: J305 Geiger-counter tube
  • Cathode material: tin oxide
  • Wall density: 50 ± 10 cg/cm²
  • Operating temperature range: -40 °C bis 50 °C
  • Diameter: 10 mm (±0,5 mm)
  • Length: 90 mm (±2 mm)
  • Self-background radiation: 0,2 pulses/s
  • Sensivity to γ-radiation: 0,1 MeV
  • Current consumption: 0,015 mA bis 0,02 mA
  • Working voltage: 380 V bis 450 V
  • γ-radiation: 20mR/h ~ 120mR/h
  • β-radiation: 100 ~ 1800 Pulse/min.
  •  100 ~ 1800 pulses/min.

The signal detection and processing of the signal also takes place on the mainboard. The recognized impulses are reproduced via a small piezo loudspeaker. In order to be able to count them, you don’t have to sit in front of the loudspeaker with a stopwatch and count the beeps every minute – no – that is done by a microcontroller, which, as is common today, consists of a finished board. Here the designer has chosen an Arduino Nano (or nano replica). In turn, a program runs on it that counts the impulses and also shows them nicely on a two-line LC display and ideally also converts them into µSievert / h. To transfer the pulses to the Arduino, the level of the signal is brought to TTL level and switched to the interrupt input of the Arduino. The LC display uses the I2C output of the Arduino. The lines for this are only led from the socket strip into which the Arduino is plugged via the mainboard to the socket strip for the display. To supply the whole system with voltage, the 5V from the USB port of the Arduino are used directly. Optionally, the 5V can also be connected to the mainboard via a connector strip.

Once everything has been assembled and the USB supply is connected, there is first of all a short waiting time during which the high voltage is built up. Here the programmer has come up with an animation that shows “Boot …” on the display.

And then it starts. The Geiger counter is ready for use and begins to count. As a test I only have an old clock with hands painted with radium paint. There is at least a clear change in the number of detected counting pulses when the watch is brought near the counter tube.

Surrounded by radioactivity?

Loading

After the self-made Geiger Müller counter and the associated experiments, I noticed that there is one or the other radioactive element in our environment.

With the SOEKS 01M Geiger counter, an industrially manufactured device, I have now again “scanned” objects in the area.

IMAG1289
SOEKS 01M

Again, I realized that some of the old clocks in my collection are equipped with radium-painted dials. The SOEKS shows here a radiation exposure of about 1.11 microSievert per hour. The environmental load is displayed at approx. 0.14 uSv / h.IMAG1290

But in my mother’s kitchen, I found a beautiful, colorful old vase that displayed about 10uSv / h. (The thing is now in the far corner of the cellar).

It should be uranium paint. (To see orange / red painting in the video below)

 

Geiger counter and radioactivity

Loading

One project that had long been of interest to me was the detection of radioactive radiation. After the horrible powerplant accidents in Japan, this idea was recalled. I could still vaguely remember owning an unused counter tube somewhere in my old workshop cellar. – After some search it turned up :). Thanks to the Internet and the search engines, a data sheet was also found quickly. The counter tube is a ZP1400. A self-extinguishing Geiger-Müller counter tube with mica window. The tube is according to data sheet with neon and argon filled as quenching gas. The operating voltage is 400 to 600V. The capacity between anode and cathode is about 2pF. With these and other information from the data sheet i now can tinker a circuit to take the tube in operation. I have used this small project to introduce our apprentice to the board layout at the same time and to get acquainted with the creation of small programs on the Arduino Uno microcontroller board. In this post I introduce only the “old-fashioned” circuit, where only the impact of ionizing radiation is made audible to the count wire. (the typical crackling). This circuit then provided the basis for the apprentice to realize the count of the pulses with the microcontroller and to visualize it on a two-line LCD.
Wiring diagram with high voltage supply and pulse amplifier

Using the well-known layout software Eagle, I have drawn a circuit in which the high voltage is again generated by a switched transformer and subsequent Greinacher cascade. The control takes over this time no 555er, but simply a feedback Schmitt trigger. The time base is set via the coupling resistor and the capacitor. Thus, the high voltage is available for the counter tube. In order to be able to count the impulses, two factors are ensured. The impulse must not exceed a certain height. (Otherwise the following electronics may die) and the pulses should be audible (boosted). So the peaks are limited with a zener diode circuit and put into a “nice” shape with Schmitt triggers and then led to an op amp. At the output of the op-amp then hangs first a small speaker …

Arrangement of components on the PCB

After the circuit board was etched and assembled, it was time to test. But with what? I needed some weak source. I held all sorts of items in front of the counter, but it did not change much. There was a cracking sound from the speaker four to eight times a minute. So I started researching the net again. And came across the term “radium color”. This is the self-luminous color with which the dials of old watches were painted, in order to be able to read the time even in the dark. This information gave me an idea. From my grandfather i inherited once an altimeter of a WW1 aircraft (manufacturer LUFFT) whose dial might have been painted with that kind of color. So get out of the showcase and held in front of the counter tube … The result can be seen in the video.